An electrochemical system is a system that either derives electrical energy from chemical reactions, or facilitates chemical reactions through the introduction of electrical energy. An electrochemical system generally includes a cathode, an anode, and an electrolyte, and is typically complex with multiple scales from nanometers to meters. Examples of these systems include batteries and fuel cells. On-line characterization of batteries or fuel cells in vehicles is difficult, due to very rough noisy environments.
On-line characterization of such electrochemical systems is desirable in many applications, which include real-time evaluation of in-flight batteries on a satellite or aviation vehicle, and dynamic diagnostics of traction batteries for electric and hybrid-electric vehicles. In many battery-powered systems, the efficiency of batteries can be greatly enhanced by intelligent management of the electrochemical energy storage system. Management is only possible with proper diagnosis of the battery states.
In many battery-powered systems such as electric vehicles and satellites, real-time characterization of battery thermodynamic potential and kinetics is desirable. The characterization is crucial for battery states estimation including the state of charge (SOC), the charge and the discharge power capabilities (state of power, SOP), and the battery state of health (SOH).
Current systems typically rely exclusively on voltage monitoring of the full battery cell, which is useful for identifying a problem but is often incapable of preventing damage because the system is triggered during/after the system has exceeded its threshold values. In these systems, the only way to completely avoid damage is to establish conservative threshold values (tighten the operating limits), which limits the performance of the battery.
A three-electrode battery structure (i.e., a battery structure that includes a reference electrode) has one more reference electrode than a conventional battery configuration, which has only two electrodes (cathode and anode). Due to this additional electrode, more current and voltage information is measurable than in conventional batteries. Therefore, a three-electrode configuration is very useful for diagnostics.
Typical in-lab experiments on three-electrode batteries are conducted around equilibrium states; therefore, the measured anode (or cathode) potential against the reference electrode is the open-circuit potential (OCV), also called thermodynamic potential, of the anode (or cathode). However, so far there hasn't been a reliable instrumentation and method to characterize each individual electrode of the battery when the battery is cycling away from equilibrium states, under a random driving profile. In many applications, such as electric vehicles, batteries are usually driven in high rates and therefore are not around equilibrium.
Methods, systems, and apparatus are sought which are capable of characterizing each individual electrode of a three-electrode battery, including open-circuit potentials, when the battery is cycling in a non-equilibrium state and under a random driving profile. What is desired is a simple, direct method of monitoring the voltage and differential voltage of each electrode independently in a battery. In a typical battery, the management system relies only on the voltage from the full cell. However, the full cell voltage is a poor indicator of the health of each electrode.